Polymastia penicillus (Montagu, 1818) is a pale greyish yellow to orange-yellow fistulose sponge growing in crevices among rocks. The main body mass is often partly buried in sediment with its fistules sticking out. It differs from its sympatric sister species P. boletiformis (= P. robusta) in its paler colour and blunt-ending, longer fistules. It is common around the British Isles and along the Atlantic coasts of France and Spain.

Taxonomic Description

Colour:The body is dirty grey; rarely orange yellow. The papillae are creamy white or pale yellow.Shape, size, surface and consistency:(polymastia_penicillus_mcs_i.jpg) A low, spreading cushion, up to l cm thick and may reach a lateral expansion of several dm2, with stiffly erect, semi-contractile papillae projecting above the sediment covered body. The hollow papillae (polymastia_penicillus_detai.jpg) are variable in number, and their length varies with age, condition and situation of the individual sponge, so that no two individuals ever look quite the same. The papillae show little tendency to fuse (contrasting with P. robusta). The sponge is firmly attached to rock beneath the sediment. The oscules and pores are carried on the cylindrical, slightly tapering papillae. The exhalant papillae are large, few in number and, with the small, terminal oscules usually open, can be distinguished easily from the smaller inhalant papillae. The pores are located towards the upper ends of the papillae, but are not obvious. The body is hard, and the papillae stiff. The surface of the body is hispid, roughened by projecting spicules which trap sediment particles, ranging from mud to fine gravel. On a few occasions when the surface is clear of sediment, the sponge may be seen enveloped in algae or bryozoans, etc. The papillae are smooth and clean; often a fine network of spicules can be seen on the surface. The body shows no contraction. The papillae are only semi-contractile and spring upright when pushed down flat. (? are these ever found to contract completely down as in P. robusta ?). Can the oscules be induced to close when touched?). Smell: None.Spicules:There is only one type of spicule: tylostyles, divided into three size groups: principal tylostyles: 725-930-1700 µm; medium-sized tylostyles of the tangential subectosomal layer: 250-540-725 µm; and small ectosomal tylostyles: 50-136-250 µm (these data are based on 2500 spicules measured by Boury-Esnault, 1974).Skeleton:(polymastia_penicillus_skel.jpg) Radiate, with a well-organised ectosome of about 500 µm in thickness. The skeleton of the papillae is continuous with that of the main body. The larger tylostyles constitute the main structural megascleres, forming stout, multispicular tracts (up to about 15 spicules thick), which run up through the choanosome and on into the papillae, partially piercing the surface. Loose spicules lie scattered between the tracts. The middle-sized tylostyles form a tangential layer of inter-crossing spicules just below the surface (2-4 spicules deep), supporting a single layer of the smallest megascleres which are arranged perpendicular to the surface, grouped into brushes. In mature sponges these spicules become more tightly packed, forming a palisade. The inhalant and exhalant canal systems are confined to the periphery of the papillae, leaving the central cavity empty. The multi-spicular tracts of long tylostyles give support to the walls of the papillae, with a similar ectosomal arrangement to that found in the body. Inhalant papillae have 6-10 tracts or bundles, exhalant papillae have 10-20 tracts, each of these consisting of 20-70 spicules in cross section.Reproduction:July till September (Lévi, 1956)Ecology:This species is often found at the sediment/bedrock interface on upward rock (rarely on boulder tops), with the body beneath a layer of sediment. Prefers conditions where some silt is held in suspension by flowing water. Its preference for silty conditions makes it more easily overlooked than P. robusta.Littoral to 2300 m. (optimum depth 5-15 m)Distribution:Arctic-Atlantic coasts of Europe and North America; Mediterranean. Recently known from many sites on the western and southern coasts of the British Isles.Etymology:The name refers to the numerous nipple-like papillae.Type specimen information:?, there are 2 dry specimens from the Norman Collection labelled "Halichondria mammillaris Johnston. Cotype." BMNH 1910.1.1.8 Norman Collection, off Guernsey, 1859 and 1910.1.1.9, Norman Collection, Polperro. These could be the "missing" genotypes?

Remarks

As stated under Polymastiamamillaris, the present species has been misnamed by most authors, since Bowerbank. P. mamillaris sensu its original author is clearly different from all these later described species recorded as P. mamillaris. Morrow & Boury-Esnault (2000) redescribed the type of P. mamillaris and proposed to name all the misnamed specimens P. penicillus. Differences between the two common Western European sympatric shallow-water species of Polymastia were tabulated by Van Soest et al., 1981: p_penicillus__p_robusta.jpg (= P. boletiformis). There are several papillate species with which smaller individuals of P. penicillus and P. boletiformis could be confused. Boury-Esnault (1987) gives a review of all Atlantic species of Polymastia and this publication may be consulted for further differences between the species.Sources: Boury-Esnault, 1974, 1987; Van Soest et al., 1981; Ackers et al., 1985.

Templeton, R., 1836. A catalogue of the species of rayed animals found in Ireland, as selected from the papers of the late J. Templeton, Esq., of Cranmore, with notices of localities, and with some descriptions and illustrations (continued from p. 422, and concluded). Radiata. Mag. Nat. Hist., IX: 466-467